I have a 6059 ARC GX390 Billet side cover. The PTO side cover seal blew out due to me installing the PVC in backwards! LOL. It actually looks okay but I'd feel safer putting a new one back in. I am fairly certain the ARC seal is thinner than the stock Honda GX 390 seal. I can't find a part number anywhere. No part number on the seal. I suppose I could call ARC on Monday, but I;d like to order today.